The invention relates to a spindle motor with magnetic seal according to the introductory parts of claims 1 and 5.
Small-sized spindle motors of this type are used especially as motors for disk storage units. These are usually collectorless DC motors, which have the problem that the bearings need to be extremely well sealed so that no oil from the bearings can penetrate into the clean air space around the motor, where the disks are located.
It is known to provide suitable sealing arrangements at the end openings between the armature and the fixed stator. In one such known arrangement, the seal may take the form of a magnetic seal essentially comprising two metal disks positioned a certain distance apart, between which a permanently magnetic disk is trapped.
A gap is thus formed on the radially inner side (i.e. towards the fixed shaft). This gap is filled with a ferromagnetic fluid, which is kept in place by the permanent magnet trapped between the two metal disks. Such a magnetic seal arrangement is known, for sealing either the upper end of the motor or the lower end of the motor, and in many cases both.
It is likewise known to use a cap, usually made of metallic material, as the outermost element of this magnetic seal. The function of this cap is to seal and protect the magnetic seal from the exterior. A known way of bringing this about is to bond such a cap into the open recess in the hub of the armature to seal it in place. This ensures that the cap, the ultimate and outermost element of the magnetic seal, will prevent foreign bodies from the exterior from getting into the magnetic seal.
Hitherto, it has moreover been known to form this cap as a disk-shaped body with a uniformly profiled rim all round. This, however, has the drawback that it is necessary to bond both the magnetic seal and, in a separate operation, the cap, thus increasing the labour cost. Moreover it takes up an excessive amount of space, as two seal arrangements (two beads of adhesive) have to be put in place, one axially superimposed above the other. This increases the overall height of the motor.
Therefore the fundamental problem which the invention seeks to solve is to develop a way of sealing the magnetic seal for a spindle motor of the kind stated in the introduction which both reduces the height required for its installation and simplifies the sealing operation so that the labour cost is reduced.
For the solution of the stated problem, the invention is characterized by the technical teaching of claims 1 and 5.
The essential feature of the invention is that both the cap and the magnetic seal are bonded to the open seat in the hub with a single bead of adhesive.
This makes it possible for the first time to greatly reduce the overall height of a spindle motor of this type by virtue of the fact that only one adhesive bead is required in the axial assembly, and not two beads needing to be placed one above the other and spaced apart.
It is achieved by shaping the cap so that it is capable of being bonded by the adhesive bead to the inner open seat in the hub and yet forms openings through which adhesive is able to flow past the outer edge of the cap to the magnetic seal beneath. Thus the radially outer rim of the cap and the radially outer rim of the underlying magnetic seal are bonded in place with a single bead of adhesive.
This is achieved by forming suitable gaps or openings at the cap""s outer edge, instead of forming it as an unbroken rim.
In a first embodiment, such gaps or openings are formed by making the rim of the cap smaller than the diameter of the inner seat, so that a gap is formed between this smaller rim and the internal diameter of the seat in the hub, and the adhesive bead is able to flow through the said gap, past the cap, to the magnetic seal beneath, and bond the rim of the upper disk of the magnetic seal to its seat in the hub.
Furthermore this is achieved by providing. lobes which project radially outwards beyond the said rim and whose outer periphery corresponds to the internal diameter of the seat in the hub.
Preferably, a plurality of radial lobes are uniformly distributed around the circumference of the cap and are integrally joined thereto. The lobes then center the cap in the central seat in the hub.
A uniform bonding gap is then obtained, as all the gaps between the inner rim of the cap and the inner circumferential face of the seat are uniformly centered, so that an even distribution of adhesive is assured.
In a preferred configuration of the present invention, instead of radially outwards pointing lobes uniformly distributed around its circumference, the cap is provided with a uniform, basically closed, peripheral rim, and, in the region of that rim, recesses, openings or slots are provided through which the adhesive is likewise able to flow to the magnetic disk beneath, to bond the edge thereof to the seat""s inner wall.
Because the adhesive essentially runs into the gaps between the cap""s outer rim and the surface of the magnetic disk beneath, the application of adhesive in the end region of this spindle motor is very thin, and this greatly reduces the overall height of the motor. The fact that adhesive is also deposited on the lobes, making a joint with the adjoining wall of the seat in the hub, is insignificant, because the adhesive which is deposited on the lobes essentially runs off the lobes to left and right and into the gaps formed between the cap and the magnetic disk beneath.
The subject-matter of the present invention is disclosed not only by the subject-matter of the individual claims, but also by the individual claims taken in combination.
All details and features disclosed in the documents (including the Abstract), and in particular the physical embodiment illustrated in the drawings, are claimed as essential to the invention, in so far as, taken separately or in combination, they are novel with respect to the state of the art.
The invention will now be described in detail with reference to drawings illustrating several ways in which the invention may be carried out. Further features essential to the invention and advantages of the invention will become apparent from the drawings and from the description thereof.